Watch Soybean Aphid Numbers - NOW

July 30, 2008

By Jon Tollefson, Department of Entomology

Last week the conditions in Minnesota were very good for soybean aphid reproduction. With those conditions, the populations increased rapidly in many locations throughout Minnesota. We have been expecting 2008 soybean aphid populations to be lower as they were in 2004 and 2006, but the 2008 weather has not been exactly “typical.”

The increase in aphid numbers in states north of us serves as a reminder that this is the time you must be scouting soybeans to avoid an outbreak of aphids in any of your soybean fields.

For some helpful reminders, the treatment threshold for soybean aphids should remain at an average of 250 aphids per plant, even with increased value of soybeans as discussed in an Integrated Crop Management article released today.

The scouting technique to monitor aphid numbers was described in an Integrated Crop Management article in July of 2007.  There is a faster, binomial method to make an aphid management decision in soybeans. The “Speed Scouting” technique is described in the article as well; additional information is available from the University of Minnesota.  A free quick field guide to using this method can be ordered from Iowa State University Extension. 


Jon Tollefson is a professor of entomology with extension and research responsibilities.

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